In a communication network capable of providing communications with guaranteed quality of service (hereunder, referred to as QoS) at a certain level or above, in order to guarantee a QoS in an actual flow transmission, it is necessary to reserve communication resources with guaranteed QoS so that the flow transmission can occupy the communication resources. This reservation is performed through, for example, a signaling mechanism such as signaling system No. 7 (SS7) in a telephone network and RSVP in an IP network. These types of conventional resource reservation signaling mechanisms control reservations for any resources so that even if all of the flows which use these resources use the entire reserved amount of the resources at the same time, these resources will not be too insufficient for a QoS guarantee to be assured.
However, in general, a flow which reserves QoS does not always constantly use all of the reserved bandwidth. For example, in those cases where the transmission process of the flow has stopped, or where the communication network has not received an amount of load for which the entire reserved resources are required, all of the reserved resources are not in use. At this time, regarding the excess resources, in those cases where these resources are exclusively reserved by a conventional signaling mechanism, resource utilization efficiency cannot be optimized as they cannot be used for another flow transmission.
As a countermeasure for this problem, there is a commonly known technique with a configuration such that when a flow is not using all of the reserved QoS resources, another flow can use the resources (for example, refer to Non-Patent Document 1). In Non-Patent Document 1, there is disclosed a technique such that in a load distribution scheduling of a link to be shared by two flows, when a minimum bandwidth is guaranteed for both flows and either one of the flows is using the minimum bandwidth or less for its bandwidth, the ratio of load distribution is dynamically changed so that the other flow can use this bandwidth.
In the technique of Non-Patent Document 1, a plurality of flows practically share a reserved bandwidth with each other to thereby realize effective utilization of available bandwidth. However, bandwidth can be shared with each other using this technique only when these plurality of flows have reserved a bandwidth of the same resources. In this case, a combination of flows which can share a bandwidth is determined by the routing of each flow.